<?xml version="1.0" encoding="UTF-8" standalone="no"?>
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
  <head>
    <meta http-equiv="Content-Type" content="text/html; charset=UTF-8" />
    <title>Adding the Replication Manager to ex_rep_gsg_simple</title>
    <link rel="stylesheet" href="gettingStarted.css" type="text/css" />
    <meta name="generator" content="DocBook XSL Stylesheets V1.73.2" />
    <link rel="start" href="index.html" title="Getting Started with Replicated Berkeley DB Applications" />
    <link rel="up" href="repapp.html" title="Chapter 3. The DB Replication Manager" />
    <link rel="prev" href="repapp.html" title="Chapter 3. The DB Replication Manager" />
    <link rel="next" href="fwrkpermmessage.html" title="Permanent Message Handling" />
  </head>
  <body>
    <div class="navheader">
      <table width="100%" summary="Navigation header">
        <tr>
          <th colspan="3" align="center">Adding the Replication Manager to
                    <span>ex_rep_gsg_simple</span>
                    
                    
            </th>
        </tr>
        <tr>
          <td width="20%" align="left"><a accesskey="p" href="repapp.html">Prev</a> </td>
          <th width="60%" align="center">Chapter 3. The DB Replication Manager</th>
          <td width="20%" align="right"> <a accesskey="n" href="fwrkpermmessage.html">Next</a></td>
        </tr>
      </table>
      <hr />
    </div>
    <div class="sect1" lang="en" xml:lang="en">
      <div class="titlepage">
        <div>
          <div>
            <h2 class="title" style="clear: both"><a id="repmgr_init_example_c"></a>Adding the Replication Manager to
                    <span>ex_rep_gsg_simple</span>
                    
                    
            </h2>
          </div>
        </div>
      </div>
      <p>
                    We now use the methods described above to add partial
                    support to the 
                    <span>ex_rep_gsg_simple</span>
                    
                    
                    example that we presented in 
                    <a class="xref" href="txnapp.html" title="Chapter 2. Transactional Application">Transactional Application</a>.
                    That is, in this section we will:
            </p>
      <div class="itemizedlist">
        <ul type="disc">
          <li>
            <p>
                                    Enhance our command line options to
                                    accept information of interest to a
                                    replicated application.
                            </p>
          </li>
          <li>
            <p>
                                    Configure our environment handle to use
                                    replication and the Replication Manager.
                            </p>
          </li>
          <li>
            <p>
                                    Minimally configure the Replication Manager.
                            </p>
          </li>
          <li>
            <p>
                                    Start replication.
                            </p>
          </li>
        </ul>
      </div>
      <p>
                Note that when we are done with this section, we will be
                only partially ready to run the application. Some critical
                pieces will be missing; specifically, we will not yet be
                handling the differences between a master and a
                replica. (We do that in the next chapter).
            </p>
      <p>
                Also, note that in the following code fragments, additions
                and changes to the code are marked in <strong class="userinput"><code>bold</code></strong>.
            </p>
      <p>
                    To begin, we copy the 
                    <span>ex_rep_gsg_simple</span>
                    
                    code to a new file called
                    <code class="literal">ex_rep_gsg_repmgr.c</code>.

                    <span>
                    We then make the corresponding change to the program name.
                    </span>

                    
            </p>
      <pre class="programlisting">/*
 <strong class="userinput"><code>* File: ex_rep_gsg_repmgr.c</code></strong>
 */

#include &lt;stdlib.h&gt;
#include &lt;string.h&gt;
#ifndef _WIN32
#include &lt;unistd.h&gt;
#endif

#include &lt;db.h&gt;

#ifdef _WIN32
extern int getopt(int, char * const *, const char *);
#endif

#define CACHESIZE   (10 * 1024 * 1024)
#define DATABASE    "quote.db"

const char *progname = <strong class="userinput"><code>"ex_rep_gsg_repmgr";</code></strong>

int create_env(const char *, DB_ENV **);
int env_init(DB_ENV *, const char *);
int doloop (DB_ENV *);
int print_stocks(DBC *); </pre>
      <p>
        Next we update our usage function. The application will continue to
        accept the <code class="literal">-h</code> parameter so that we can identify
        the environment home directory used by this application. However,
        we also add the 
</p>
      <div class="itemizedlist">
        <ul type="disc">
          <li>
            <p>
                    <code class="literal">-l</code> parameter which allows us to
                    identify the host and port used by this application to
                    listen for replication messages.
                </p>
          </li>
          <li>
            <p>
                        <code class="literal">-r</code> parameter which allows us to
                        specify other replicas.
                </p>
          </li>
          <li>
            <p>
                        <code class="literal">-n</code> parameter which allows us to
                        identify the number of sites in this replication
                        group.
                </p>
          </li>
          <li>
            <p>
                    <code class="literal">-p</code> option, which is used to identify
                    this replica's priority (recall that the priority is
                    used as a tie breaker for elections)
                </p>
          </li>
        </ul>
      </div>
      <pre class="programlisting">/* Usage function */
static void
usage()
{
  fprintf(stderr, "usage: %s ", progname);
  fprintf(stderr, "-h home <strong class="userinput"><code>-l host:port -n nsites</code></strong>\n");
  <strong class="userinput"><code>fprintf(stderr, "\t\t[-r host:port][-p priority]\n");
  fprintf(stderr, "where:\n");
  fprintf(stderr, "\t-h identifies the environment home directory ");
  fprintf(stderr, "(required).\n");
  fprintf(stderr, "\t-l identifies the host and port used by this ");
  fprintf(stderr, "site (required).\n");
  fprintf(stderr, "\t-n identifies the number of sites in this ");
  fprintf(stderr, "replication group (required).\n");
  fprintf(stderr, "\t-r identifies another site participating in ");
  fprintf(stderr, "this replication group\n");
  fprintf(stderr, "\t-p identifies the election priority used by ");
  fprintf(stderr, "this replica.\n");</code></strong>
  exit(EXIT_FAILURE);
} </pre>
      <p>
        Now we can begin working on our <code class="literal">main()</code> function.
        We begin by adding a couple of variables that we will use to
        collect TCP/IP host and port information. 


        <span>
        We also declare a couple
        of flags that we use to make sure some required information is
        provided to this application. 
        </span>
</p>
      <pre class="programlisting">int
main(int argc, char *argv[])
{
    extern char *optarg;
    DB_ENV *dbenv;
    const char *home;
    char ch, <strong class="userinput"><code>*host, *portstr</code></strong>;
    int ret, <strong class="userinput"><code>local_is_set, totalsites</code></strong>;
    <strong class="userinput"><code>u_int32_t port</code></strong>;

    dbenv = NULL;

    ret = <strong class="userinput"><code>local_is_set = totalsites = </code></strong>0;
    home = NULL; </pre>
      <p>
        At this time we can create our environment handle and configure it
        exactly as we did for <code class="literal">simple_txn</code>.  
        The only thing that we will do differently here is that we will set a priority,
        arbitrarily picked to be 100, so that we can be sure the environment has
        a priority other than 0 (the default value). This ensures that the
        environment can become a master via an election.
</p>
      <pre class="programlisting">    if ((ret = create_env(progname, &amp;dbenv)) != 0)
            goto err;

    /* Default priority is 100 */
    <strong class="userinput"><code>dbenv-&gt;rep_set_priority(dbenv, 100);</code></strong>   </pre>
      <p>
        Now we collect our command line arguments. As we do so, we will
        configure host and port information as required, and we will
        configure the application's election priority if necessary.
</p>
      <pre class="programlisting">    /* Collect the command line options */
    while ((ch = getopt(argc, argv, "h:<strong class="userinput"><code>l:n:p:r:</code></strong>")) != EOF)
        switch (ch) {
        case 'h':
            home = optarg;
            break;
        <strong class="userinput"><code>/* Set the host and port used by this environment */
        case 'l':
            host = strtok(optarg, ":");
            if ((portstr = strtok(NULL, ":")) == NULL) {
                fprintf(stderr, "Bad host specification.\n");
                goto err;
            }
            port = (unsigned short)atoi(portstr);
            if (dbenv-&gt;repmgr_set_local_site(dbenv, host, port, 0) 
                                                              != 0) {
                fprintf(stderr,
                    "Could not set local address %s.\n", host);
                goto err;
            }
            local_is_set = 1;
            break;
        /* Set the number of sites in this replication group */
        case 'n':
            totalsites = atoi(optarg);
            if ((ret = dbenv-&gt;rep_set_nsites(dbenv, totalsites)) 
              != 0)
                dbenv-&gt;err(dbenv, ret, "set_nsites");
            break;
        /* Set this replica's election priority */
        case 'p':
            dbenv-&gt;rep_set_priority(dbenv, atoi(optarg));
            break;
        /* Identify another site in the replication group */
        case 'r':
            host = strtok(optarg, ":");
            if ((portstr = strtok(NULL, ":")) == NULL) {
                fprintf(stderr, "Bad host specification.\n");
                goto err;
            }
            port = (unsigned short)atoi(portstr);
            if (dbenv-&gt;repmgr_add_remote_site(dbenv, host, port, 
                                                 NULL, 0) != 0) {
                fprintf(stderr,
                    "Could not add site %s.\n", host);
                goto err;
            }
            break;</code></strong>
        case '?':
        default:
            usage();
        }

    /* Error check command line. */
    if (home == NULL <strong class="userinput"><code>|| !local_is_set || !totalsites</code></strong>)
        usage(); </pre>
      <p>
            Having done that, we can call <code class="function">env_init()</code>, which we use to 
        open our environment handle. Note that this function changes
        slightly for this update (see below).
    </p>
      <pre class="programlisting">    if ((ret = env_init(dbenv, home)) != 0)
        goto err; </pre>
      <p>
        Finally, we start replication before we go into the 
        <code class="function">doloop()</code> function (where we perform all our
        database access). 
</p>
      <pre class="programlisting">
    <strong class="userinput"><code>if ((ret = dbenv-&gt;repmgr_start(dbenv, 3, DB_REP_ELECTION)) != 0)
        goto err; </code></strong>

    if ((ret = doloop(dbenv)) != 0) {
        dbenv-&gt;err(dbenv, ret, "Application failed");
        goto err;
    }

err: if (dbenv != NULL)
        (void)dbenv-&gt;close(dbenv, 0);

    return (ret);
} </pre>
      <p>
            <span>Beyond that, the rest of our application remains the same for
            now, with the exception of the <code class="function">env_init()</code>
            function, which we use to actually open our environment handle.
            The flags </span>

            

            

            we use to open the environment are slightly different for a
            replicated application than they are for a non-replicated
            application. Namely, replication requires the
            <span>
            <code class="literal">DB_INIT_REP</code> flag. 
            </span>

            
    </p>
      <p>
            Also, because we are using the Replication Manager, we must prepare
            our environment for threaded usage. For this reason, we also
            need the <code class="literal">DB_THREAD</code> flag.
    </p>
      <pre class="programlisting">int
env_init(DB_ENV *dbenv, const char *home)
{
    u_int32_t flags;
    int ret;

    (void)dbenv-&gt;set_cachesize(dbenv, 0, CACHESIZE, 0);
    (void)dbenv-&gt;set_flags(dbenv, DB_TXN_NOSYNC, 1);

    flags = DB_CREATE | 
            DB_INIT_LOCK | 
            DB_INIT_LOG | 
            DB_INIT_MPOOL |
            <strong class="userinput"><code>DB_INIT_REP |</code></strong>
            DB_INIT_TXN | 
            DB_RECOVER <strong class="userinput"><code>|
            DB_THREAD;</code></strong>
    if ((ret = dbenv-&gt;open(dbenv, home, flags, 0)) != 0)
        dbenv-&gt;err(dbenv, ret, "can't open environment");
    return (ret);
}</pre>
      <p>
        This completes our replication updates for the moment. We are not as
        yet ready to actually run this program; there remains a few
        critical pieces left to add to it. However, the work that we
        performed in this section represents a solid foundation for the
        remainder of our replication work.
    </p>
    </div>
    <div class="navfooter">
      <hr />
      <table width="100%" summary="Navigation footer">
        <tr>
          <td width="40%" align="left"><a accesskey="p" href="repapp.html">Prev</a> </td>
          <td width="20%" align="center">
            <a accesskey="u" href="repapp.html">Up</a>
          </td>
          <td width="40%" align="right"> <a accesskey="n" href="fwrkpermmessage.html">Next</a></td>
        </tr>
        <tr>
          <td width="40%" align="left" valign="top">Chapter 3. The DB Replication Manager </td>
          <td width="20%" align="center">
            <a accesskey="h" href="index.html">Home</a>
          </td>
          <td width="40%" align="right" valign="top"> Permanent Message Handling</td>
        </tr>
      </table>
    </div>
  </body>
</html>
